Saying 'Iqra`' to someone is to order them to read. When Prophet Muhammed (SAW) was meditating in the cave of hiraa he was ordered to read by angel Jibraeel (Gabriel). Iqra` was the first word of the Quran that came upon the Prophet (SAW).
The angel repeated the order: iqra! Read! as Muhammed explained he was unable to read, then Jibraeel said:
[96.1] Read in the name of your Lord Who created.
[96.2] He created man from a clot.
[96.3] Read and your Lord is Most Honorable,
[96.4] Who taught (man to write) with the pen
[96.5] Taught man what he knew not.
These are the first verses of the Quran that came down to the Prophet.